1. Field of the Invention
This invention pertains to gamma imaging devices and more particularly to that class of device known as scintillation cameras.
In the diagnosis of certain illnesses, radioactive isotopes are administered to patients. Many administered isotopes have the characteristic of concentrating in certain types of tissue and either not concentrating in or concentrating to a lesser degree in other types of tissue. For example, iodine 131 collects in thyroid glands. A graphic image produced to show the spatial distribution and concentration of this isotope in the thyroid gland provides an image of the thyroid gland itself. This image is useful in diagnosing a patient's physical condition.
2. Summary of the Prior Art
Generally speaking, the devices used for producing graphic images of the distribution of an isotope in a subject are known as scanners and cameras. With a scanner, a scintillation probe is moved rectilinearly along a plurality of spaced parallel paths. The energy detected is utilized to make either a photographic or a dot image reflecting the spatial distribution and concentration of the isotope in the subject. A clinically successful scanner is described in greater detail in the above-referenced U.S. Letters Pat. No. Re. 26,014 to J. B. Stickney et al.
The devices known as cameras remain stationary with respect to the patient as the graphic image of the spatial distribution of an isotope is developed. Many cameras use an instrument where a relatively large disc-like scintillation crystal is positioned to be bombarded by gamma radiation emitted by a patient. With most cameras, a collimater is interposed between the patient and the crystal. The crystal converts the gamma ray energy impinging on it to light energy. This light energy is in the form of light flashes or scintillations. In one class of camera, a thalium-activated sodium iodide crystal is typically utilized. Since sodium iodide is highly hygroscopic, it is encapsulated with an hermetically sealed envelope. A plurality of phototubes are positioned near the crystal. When a phototube detects a scintillation, an electrical signal is emitted by the phototube. The electrical signal emitted by the phototube is of an intensity which is proportional both to the intensity of the light flash and its distance from the phototube.
Signals emitted simultaneously by the camera phototubes are amplified and then conducted to electronic circuitry. The preferred circuitry is described in greater detail in the referenced applications. This circuitry includes a pulse-height analyzer to determine whether ot not the signals in question reflect the occurrence of a so-called photopeak event. Summing and ratio circuits are included which result in the signal being sent to an oscilloscope to cause a light signal to be emitted by the oscilloscope. The objective is that the oscilloscope signals be displaced relatively each at a location corresponding to the location of a corresponding scintillation in the crystal.
It is a general object of the present invention to provide a more versatile camera than has heretofore been available.
It is a more specific object to provide such an instrument that is capable of resolving radiation emanating from either one or both of two radioactive isotopes and displaying a graphic image of the spatial distribution of radiation from either isotope or of both isotopes.
It is a further object to provide an instrument that incorporates recording and playback apparatus, and that incorporates an improved technique for calibrating the phototube section of the instrument.